1. Field of the Invention
The present invention concerns tires and, in particular, the arrangement of the carcass cord and their anchoring in the beads.
2. The Related Art
WO 98/54006 recently proposed a new type of carcass reinforcement of a tire and its anchoring in its bead. A tire, according to this application, contains a crown, two sidewalls and two beads, a carcass reinforcement with first reinforcing cords placed adjacent, aligned circumferentially in at least one circumferential alignment from a bead to a sidewall and anchored in said bead, and a crown reinforcement, each of the beads containing an anchoring zone enabling the carcass reinforcement to be maintained and including at least one circumferentially oriented second reinforcing cord cooperating with an adjacent portion of the carcass reinforcement by means of a rubber anchoring compound. This rubber anchoring compound has a modulus of elasticity at a 10% deformation greater than 20 MPa and preferably greater than 30 MPa.
This new architecture of the tire beads gives excellent results, notably, as far as fatigue is concerned. The applicants found, however, that the marked rigidity of those beads could entail difficulties with mounting and demounting the tires, notably, on manual mountings and demountings, for large-sized tires, such as truck tires.
The present invention is intended to solve that problem.
In the text that follows:
“cord” means monofilaments as well as multifilaments, or assemblages like cords, yarns or else any type of equivalent assemblage, regardless of the material and treatment of these cords, such as surface treatment or coating or presizing in order to promote adhesion to the rubber;
“contact” between a cord and a rubber anchoring compound means the fact that at least a part of the outer circumference of the cord is in close contact with the rubber anchoring compound; if the cord contains a covering or a coating, the term contact means that it is the outer circumference of that covering or coating which is in close contact with the rubber anchoring compound;
“axial” means a direction parallel to the axis of rotation of the tire; that direction can be “axially inner” when it is directed toward the inside of the tire and “axially outer” when it is directed toward the outside of the tire;
“radial” means a direction passing through the axis of rotation of the tire and normal to the latter; that direction can be “radially inner” or “radially outer” depending on whether it is directed toward the axis of rotation of the tire or toward the outside of the tire;
“modulus of elasticity” of a rubber compound means a secant modulus of extension at 10% deformation and at room temperature; the measurement is made after a first cycle of accommodation to 10% deformation;       E    10    =                              F          10                          S          ×                      ɛ            10                              ⁢                           ⁢              i        .        e        .                                   ⁢                  E          10                      =                                                      F              10                        ⁡                          (                              1                +                                  ɛ                  10                                            )                                                          S              0                        ×                          ɛ              10                                      ⁢                                   ⁢        a        ⁢                                   ⁢        n        ⁢                                   ⁢        d        ⁢                                   ⁢                  E          10                    =                                    F            10                    ×          1.1                                      S            0                    ×          0.1                    where ε10 is equal to 0.1
with E10: secant modulus of extension at 10% extension; F10: extension force at 10% extension; So: initial section of the test sample or piece; S: section of test sample at extension ε, for rubber material,       S    =                  S        0                    1        +        ɛ              ;and ε10: extension at 10%.
“Tg” of an elastomer means the vitreous transition temperature of the latter measured by differential thermal analysis;
“static creep test” means a test in which test pieces are prepared, the useful part of which has a length of 70 mm, a width of 5 mm and a thickness of 2.5 mm (those test pieces are cut into vulcanized plates 2.5 mm thick); the test pieces are placed in an oven at 150° C. and a weight of 3 kg is immediately coupled to them; the test is thus carried out with an initial strain of:       σ    0    =                    M        ×        g                    S        0              =          2.35      ⁢      Mpa      
with M: weight applied; g: acceleration due to gravity; and S0: initial section of the measuring test piece; the elongation of the useful part of the test piece is measured as a function of time; the “static creep rate” corresponds to the variation of deformation in a given time, for example, between 3 and 5 test hours:   τ  =      Δɛ          Δ      ⁢                           ⁢      t      
with: Δε=ε(t2)−ε(t1) variation of deformation measured during Δt=t2−t1 in minutes (min);
“rheometry test”: an alternate shear test at a deformation of ±0.2 degree, a frequency of 100 cycles/min, a temperature of 197° C. and a duration of 10 min; Monsanto rheometer; the test is carried out on a raw compound disk; the development of the torque resulting from the shear imposed between the two faces of the disk is registered for 10 min.; the development of the torque is particularly noted here after the maximum measured; if the torque measured remains stable, there is no reversion, that is, diminution of stiffness of the test piece; if the torque measured diminished, it is indicated that there is a reversion; the reversion phenomenon expresses a diminution of rigidity of the test piece under the test conditions; this is a test of thermal stability of the compound at high temperature; one observes:   r  =                              C          max                -                  C          10                            C        max              *    100  
r is the reversion rate following the test; Cmax is the maximum torque measured and C10 is the torque measured after 10 min. of test;
“a circumferentially oriented cord” means a cord oriented roughly parallel to the circumferential direction of the tire, that is, forming an angle with that direction not departing by more than five degrees from the circumferential direction; and
a “radially oriented cord” means a cord roughly contained in the same axial plane or in a plane forming an angle less than or equal to 10 degrees with an axial plane.